Metallization of electrically nonconductive fabrics, fibrous materials, and porous materials



Patented June 28, 1949 METALIJIZATION OF ELECTRJCALLY NON- CONDUCTIVE FABRICS, FIBROUS MATE- RIALS, AND POROUS MATERIALS Charles T. Sucliy, London, England No Drawing. Application No. 581,169. In Great Britain February 29,

March .5, 1945, Serial Section 1, Public Law 690, August 8, 1946 Patent expires February 29,1964

4 Claims.

This invention relates to the metallisation of bodies of non-conductive porous material including non-conductive fabrics such as cotton, artificial silk and the like, and fibrous or porous materials such as .felt, paper, Wood, porcelain and the like, by electro-deposition.

Suggestions have doubtless been made in the past for coating various non-conducting materials with metals which have involved the treatment of the surfaces with conducting material and then electro-depositing upon the conducting surface another metal such as copper.

All prior suggestions have failed in practice for the reason that the rendering of the surface of the material conductive only results in a superficial deposit at and above the surface with the inevitable consequence that the deposit does not adhere with sufficient firmness to render the material useful for any practical purpose.

The present invention differs fundamentally from all prior proposals known to us in that it involves as an essential the treatment of the material, in such a way that its internal structure is impregnated with metallic particles so as to render it conductive while its surfaces are rendered as non-conductive as possible, prior to the electro-deposition treatment. That is to say, the present invention is based upon the conception that, to attain success, you must proceed in the opposite direction to the teaching of the prior art and be sure that, prior to the electro-deposition treatment, while the internal structure of the material is rendered conductive its surface or surfaces are rendered substantially non-conductive so that the growth of the electro-deposit commences within the structure and beneath the surface or surfaces and becomes interlocked with the structure of the material and only if the electro-deposition process is continued sufliciently long will the surface or surfaces ultimately become covered.

The invention consists broadly of a process for the metallisation of non-conductive fabric and fibrous or porous material according to which the internal structure of the material is first rendered electrically conductive and the external surface or surfaces is or are treated to ensure that such surface or surfaces is or are rendered as nonconductive as possible and the material so pre treated is then subjected to electro-deposition whereby the electro-deposited metal is first deposited within the structure of the material and beneath its surface or surfaces and only extends to cover the surface or surfaces if the electrodeposition process is continued for a sufficient time period.

The invention further comprises an optional final treatment according to which the material is subjected to a second electro-deposition process.

Where for example it is desired to apply to the fabric, initially plated with one metal, such as copper, another metal such as gold or silver, the copper coatin can be utilised, as .a matter of economy, as an intermediate base upon which a very thin coating of the noble metal can then be applied.

In such a case the final product would be the material chemically impregnated with conducting metal particles, a copper layer and a further layer of the noble metal.

In carrying out the process according to the preferred method the material is, if necessary, first degreased, for example by treatment with trichlorethylene followed by washing with hot water and final thorough rinsing or cleansing in water.

The cleaned material is then treated by immersion in a catalyser such as stannous chloride, after which it is impregnated by immersion in a colloidal silver solution consisting of silver nitrate dissolved in an aqueous solution of ammonia. to which is added caustic potash, the resulting precipitate being then redissolved in an ammonia solution. To this silver solution a percentage of a reducing solution composed of sugar dissolved in distilled water and heated with nitric acid is added.

The fabric or fibrous material being treated is preferably kept in motion in the combined solution or the solution suitably agitated.

It will be found that the reaction will be com- I pleted in from 20 to 30 minutes.

In some cases this impregnation treatment may be repeated to ensure a high degree of conductivity. The now conductive material is thoroughly washed and thoroughly dried and the metallic particles on the surface of the material brushed off or otherwise removed.

This removal of the metallic particles is of paramount importance and the ideal condition is met when all these particles are removed so that the surface is rendered completely free of any conductive particles but it will be understood that a few isolated particles which may inadvertently be allowed to remain on the surface after the drying and brushing operation will not interfere with the success of the process since the surface will still remain substantially, if not completely,-

the first deposit will usually be copper, the quantity deposited depending upon the particular purpose for which the fabric is required. It is recommended that where copper is to be deposited the material be flashed with copper cyanide in accordance with known practice prior to the electro-deposition treatment.

In the practice of the process it is, of course, inevitable that when introduced into the electrolytic bath moisture will be absorbed. For this reason, particularly if the material be relatively thick, it is desirable to proceed in stages and remove the material from the electrolytic bath and dry it, from time to time, and when the material is to be polished by buffing it is important that the material be thoroughly dried after the electrolytic deposition and prior to the polishing, as experience has shown that while there is a degree of porosity in a skin of electro-deposited metal, prior to polishing, which will permit the escape of any moisture beneath it, after polishing the minute pores in the skin are closed up by the polishing operation.

Thus, in cases where a thick deposit is desired the material should be removed from the bath as soon as the deposit has built up to the surface to form an adherent and coherent skin. The material should then be thoroughly dried, or allowed to dry, and then polished to close up the pores in the deposited skin. The material can then be again introduced into the electrolytic bath and the electro-deposition completed without fear of the material absorbing any further moisture.

Experiment has shown that fibrous or porous materials such as felt, soft wood, porcelain or the like, however thick, can be successfully treated if any polishing is deferred until the material is thoroughly dry. If only a thin skin of the deposited metal is required the deposit will be found to be quite firmly adherent. If a thicker skin is required the polished material can, as before indicated, be reintroduced into the electrolytic bath and any thickness of deposit safely built up. In the case of woven fabrics the deposited skin will usually be very thin and no polishing will be required.

By way of explanation, but not of limitation, it can be said that the following solutions have proved satisfactory in carrying out the process according to the preferred method.

The catalyser consisted of an aqueous stannous chloride solution composed of 2.3 grammes of stannous chloride in 1 litre of distilled water.

The colloidal silver solution consisted of 200 grammes of silver nitrate dissolved in 1 litre of distilled water to which was added an aqueous solution of ammonia of specific gravity of .85 to .99 until the initial precipitate dissolved. There was then added 100 grammes of caustic soda and the precipitate formed was redissolved in about 100 c. c. of the above ammonia solution to which was added litres of distilled water.

.4 The reducing solution was composed of grammes of commercial sugar dissolved in 500 c. c. of distilled water. 4 c. c. of nitric acid of specific gravity of 1.4 was added and the mixture heated until all the sugar had dissolved. After the solution had been allowed to cool to normal temperature it was made up to 1 litre.

In the electrolytic process, particularly at the commencement, very low current densities should be employed and we have found that A.; ampere per square decimeter of surface at 1 to 2 volts proves satisfactory. After an initial skin has been deposited the current can be increased to one ampere and the voltage to from 4 to 6 and the deposit encouraged by the application of heat and agitation in accordance with known electrolytic practice.

The wide application of the invention will be well understood, the process lending itself interalia to the production of industrial products such as electrical conductors and screens, filtering gauzes, metallised paper and decorative articles such as gilded and silvered fabrics and braid.

I claim:

1. Process for the metallization of electrically non-conductive fabrics, electrically non-conductive fibrous materials, and electrically non-conductive porous materials, which process comprises rendering the internal structure of the material electrically conductive by immersing the material in a colloidal silver solution to which is added a reducing solution to deposit metallic silver within the internal structure of the material being treated; thoroughly drying the material, and then brushing the surface thereof to rid the same of any metallic silver deposited thereon and restore the surface of the material to its initial nonconductive state; then subjecting the material to electro-deposition in an electrolytic bath, drying to rid the material of all moisture, and finally polishing to close the pores of the electrodeposited metal.

2. Process for the metallization of electrically non-conductive fabrics, electrically non-conductive fibrous materials, and electrically non-conductive porous materials, which process comprises immersing the material in a colloidal silver solution, containing a reducing agent, to deposit metallic silver within the internal structure of the material being treated, thoroughly drying the material, and then brushing the surface thereof to rid the same of any metallic silver deposited thereon and restore the surface of the material to its initial non-conductive state; immersing the material in an electrolytic bath and subjecting to electro-deposition, drying to rid the material of all moisture, polishing to close the pores of the electro-deposited metal; electro-depositing a different metal upon the polished surface of the first electro-deposited metal, drying to rid of all moisture, and then polishing to close the pores of the metal last deposited.

3. Process for the metallization of electrically non-conducting fabrics, fibrous materials and porous materials, which process comprises immersing the material in a stannous chloride solution; rendering the internal structure of the pretreated material electrically conductive by immersing the material in a colloidal silver solution to which is added a reducing solution to deposit metallic silver Within the internal structure of the material, thoroughly drying the material and brushing the surface thereof to rid the same of any metallic silver deposited thereon and restore 7 the surface of the material to its initial non-conductive state, and with the surface of the material in this non-conductive state subjecting the material to electro-deposition in an electrolytic bath.

4. Process for the metallization of electrically non-conducting fabrics, fibrous materials and porous materials, which process comprises immersing the material in a stannous chloride solution; rendering the internal structure of the pretreated material electrically conductive by immersing the material in a colloidal silver solution to which is added a reducing solution to deposit metallic silver within the internal structure of the material; thoroughly drying the material and brushing the surface thereof to rid the same of any metallic silver deposited thereon and restore the surface of the material to its initial nonconductive state; and with the surface of the material in this non-conductive state, subjecting the material to electro-deposition in an electrolytic bath, drying to rid the material of all moisture, and then polishing to close the pores of the electro-deposited metal.

CHARLES T. SUCHY.

REFERENCES CITED The following references are of record in the file of this patent: 

